Method of refining uranium



VOct. 9, 1956 l G. MEISTER V'2,755,110

METHOD OF REFINING URANIUM Filed March 8, 1944 /NRT GAS FEED CARBON gli l g ROD ;;:l f F055@ JT/RRER JAU- BATH muc/BLE g /-cAA 0v/v E HIGH FREQUENCY HfA TER cof/ E E mlmll URAA//UMMEML :Hi:

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METHOD OF REFINING URANIUM George Meister, Newark, N. J., assignor to the United States of America as represented by the United States Atomic Energy Commission Application March s, 1944, serial No. 525,601

' 3 claims. (c1. 'ls-sal) This invention relates -to the refining of uranium and more particularly to a method of refining and purifying uranium powder produced by electrolysis or produced by other reduction processes.

Methods and apparatus for the recovery of uranium by the electrolysis of uranium compounds in a fused salt bath are disclosed in copending application Serial No. 478,270, led March 6, 1943, by William C. Lilliendahl et al., now United States Letters Patent N-o. 2,690,421, issued September 28, 1954. Brieliy, the method thereof includes the electrolysis of a uranium halide in a fused salt bath in which uranium is deposited on a cathode in the -form of a powder, the rening of the uranium powder to free it of soluble impurities by grinding and washing operati-ons, and finally the compression of the uranium powder into a slug or button. The present invention relates to improvements lin methods of refining uranium, particularly electrolytically deposited uranium powder, such as the uranium deposits produced by the methods and apparatus of said application.

Uranium metal prepared by electrodeposition from a fused salt bath is generally in the form of powder containing more or less impurities including uranium oxide, metals, and salts from the fused bath. As set forth in the above-mentioned application, such powdered uranium may be refined and puried by a series of crushing, Washing, grinding, drying, sintering and fusing operations to obtain a body of coalescent uranium suitable for commercial uses.

The present invention discloses that impure uranium may be refined and purified -by treatment at high temperatures in a fused salt bath to remove oxides, salts and any other impurities. An alkali acid fluoride bath, such as potassium acid |fluoride 'is found to be particularly effective.

It is the object of this Iinvention to provide a method of relining and purifying uranium by separating the impurities from the uranium while simultaneously fusing the pure metal s-o produced.

It is an object of this invention to provide a method gf fusing uranium powder to obtain uranium in coalescent or-m.

It is another object of this invention to provide a method using a fused salt bath for purifying and fusing uranium powder.

I-t is still another object of this invention to provide a fused salt bath for refining impure uranium lat temperatures above the melting point of uranium.

Other objects and advantages of the invention will be readily apparent to those skilled in the art from the following description of preferred methods and bath compositions embodying the invention.

The drawing is illustrative of apparatus which may be employed in practicing the method which constitutes the subject matter of the present invention.

According to the method of the present invention, uranium powder, such as that produced eleetrolytically nited States Patent- Pice in accordance With the disclosure of said copending application, is rened in a fused salt bath at temperatures above the melting point of uranium. The uranium to be refined may be the electrodeposited powder, as mentioned above, or it may be uranium produced by other methods and/or uranium partially -rened by crushing, Washing, sintering, fusing or similar operations. The fused salt bath may include sodium chloride, NaCl, calcium chloride, CaClz, barium chloride, VBaClz, sodium fluoride, Nal?, calcium uoride, CaFz, barium fluoride, BaFz, or magnesium fluoride, MgFz, and the like, alone or in combination. A particularly suitable bath conttt-ins a potassium acid fluoride, such as KHFz, in combination with another halide, such as barium chloride, BaClz. The ratio of the acid uoride to the halide is not critical except that the mixture should be such as to be fused and remain molten lat temperatures of the order of l000 to l200 C. in order to be molten at temperatures above the melting point of uranium metal. An acid uoride bath appears to be more satisfactory than a straight fluoride bath, possibly because of better heating and because the acid uoride more readily dissolves the oxide impurities. The temperature of the ba-th should be maintained -at about 1100 to 1200 C. during the refining operation by any suitable means such Aas by resistance heating or by high frequency induction heating in .the event that the heat capacity of the bath is insufhcient 'to maintain a temperature above the melting point of uranium long enough for the impurities to be separated from the uranium.

The preferred method of this invention includes the steps of heating .the mixture of salts until a fused bath having a temperature of 1000" to 1100 C. is attained, adding the impure uranium -to be rened to the fused bath, raising the temperature of the fused mixture to approximately 1200 C., and maintaining said temperature for about ten minutes while stirring the mixture with a carbon rod. Similar methods, such as adding the fused salts to the impure uranium, or fusing the sal-ts and uranium together in an inert gas or in vacuum, may also be used. 'The described Atreatment apparently refines the impure uranium by vaporizing certain impurities and by converting other impurities into products which vaporize and/or products which dissolve or remain in the bath mixture. While the refining operation may be conducted successfully in air, the presence of a circulated inert gas or a vacuum is advantageous to carry away the volatile impurities including volatile uorides. The particles of uranium fuse and coalesce in the salt bath to form pure uranium in coalescent form. The fused uranium may be allowed to solidify in the bottom of the crucible under a layer of slag and a layer of salt, and may be subsequently recovered by breaking open the crucible. The fused uranium may also be recovered by being tapped from the bottom of the Crucible and cast in a suitable m-old or molds.

By use of the methods and compositions set forth above, uranium in either the powder form or a dense form may be easily refined to produce fused uranium in coalescen-t condition free of oxide and salt impurities and free of metals such as metallic sodium. The novel method disclosed is particularly economical since it eliminates crushing, washing, grinding, sintering, and simil-ar steps, and eliminates the losses inherent in such steps.

Various changes and substitutions may be made in the methods and compositi-ons described without departing from the spirit and scope of my invention as defined in the following claims.

I claim:

1. The method of refining uranium which comprises the steps of preparing a fused bath containing essentially a potassium acid uoride and barium chloride, heating 3 4 said 'bath to a temperature of approximately 1100 C. to References Cited in the le of this patent 1200 C., -adding impure uranium to said fused bath, and UNITED STATES PATENTS collecting substantially pure uranium in coalescent form under Said bath 1,180,435 RObSOll Apr. 25, 1916 3. The method of refining uranium which comprises 230865 Great Bmtam Dec' 10 1925 the steps of preparing a fused bath containing essentially 15 OTHER REFERENCES a mixture of a potassium acid liu-oride and barium Chlo; Goggin. Cronin, Fogg, James: Industrial and Em ride, heating said -batli -to a temperature of about 1100 gineering Chemistry, Fell 1926 pp. 114 116 fo 1200 C addmg 'impure Uranium Powder Produced w. Kroll; Zeitschrift fr Metaukunde, Feb. 1936,

by electrolysis to said bath while maintaining a ow of p an inert gas over the surface of said bath, and collecting 20 substantially pure uranium in coalescen't for-rn under said bath. 

1. THE METHOD OF REFINING URANIUM WHICH COMPRISES THE STEPS OF PREPARING A FUSED BATH CONTAINING ESSENTIALLY A POTASSIUM ACID FLUORIDE AND BARIUM CHLORIDE, HEATING SAID BATH TO A TEMPERATURE OF APPROXIMATELY 1100* C. TO 1200* C., ADDING IMPURE URANIUM TO SAID FUSED BATH, AND COLLECTING SUBSTANTIALLY PURE URANIUM IN COALESCENT FORM UNDER SAID BATH. 